Many high power applications require the use of high voltage semiconductor devices, such as a drain extended metal oxide semiconductor (DEMOS), because of their lower specific resistance, faster switching speed and lower gate drive power dissipation than their bipolar counterparts. Certain important characteristics of a DEMOS include its specific resistance, its breakdown voltage as well as its safe operation area (SOA). It is desirous to have a lower specific resistance and a higher breakdown voltage. The breakdown voltage of a DEMOS may be improved by adjusting the drift region of the device. A semiconductor device having a drift region with a doping concentration that increases towards the drain region would have a higher breakdown voltage.
In some conventional semiconductor devices, the drift region has a uniform doping concentration between a gate electrode and a drain implant of the device. Furthermore, the formation of some conventional semiconductor devices are susceptible to misalignment in silicide block and drain implant masking steps, which produce large variations in breakdown voltage and specific resistance.